It is known to provide aquariums with a combination of mechanical, chemical and biological filtration to maintain water quality. The correct combination of these methods will remove most organic waste and help maintain a healthy environment within the aquarium.
Heretofore different types of organic deposits have been removed from aquariums utilizing foam fractionation induced within a column in which air bubbles injected into the water within the column collect hydrophilic molecules of surfactants and carry them to the water surface to create a removable foam. As is known in the art, many of the organic substances such as protein deposits within an aquarium are surface active polar molecules which will bond to the surface of bubbles. As the bubbles rise through the water, they carry the bonded surface active material with them to form a surfactant-containing foam at the water surface. If the foam on the surface of the water is stable, the water drains away therefrom and the foam and protein deposits contained therein are thus separated from the water and can easily be removed.
Effective foam fractionation cleansing of aquarium water depends upon the nature of the foam produced by the water/bubble counterflow in the contact column. The foam must have sufficient stability to allow the water to drain away from the foam formation at the water surface without draining away the surfactants. Foam drainability is affected by foam bubble size, viscosity, and surface tension. Foam stability requires that the film concentration of the surface layer be different from that of the water, and that the surface layer be of high viscosity. Small bubbles are more effective for adsorption of organic surfactants than larger ones for a given volume of air introduced into the water because of their greater cumulative surface area. However, the bubbles should not be so small that they are unable to break the surface tension at the air-water interface to form foam on the surface of the water. Optimal values of these factors result in a surface film concentration which is different from that of the bulk liquid (the water of the aquarium) and a high viscosity in the surface layer so that the collected impurities can be removed therefrom.
In one known foam fractionation skimming device, air is injected through a bubble-forming gas discharge device such as an air stone at or near the bottom of a column of water. The bubbles rise up through the column, collecting molecules of polar surfactants along the way, and congregating at or above the water surface to form a foam layer within the column which contains the surfactant molecules. A cup fitted on the top of the column collects the foam through a center opening and is then removed for cleaning. Water is drawn through the bottom of the column and carried upward within the column by the rising air bubbles and is discharged through other openings in the column wall. The foam fractionation produced by using an air line only to induce bubble and water flow through the column is limited by insufficient counterflow of water and bubbles.
In another known type of foam fractionation skimming device, water is drawn from a tank or aquarium and directed into a water column by a pump connected through the side of the column below the water surface. An air line is connected to an outlet of the pump so that the motion of the water pumped past the air line opening draws air into the pumped water flow by a quasi-venturi effect. The air drawn in by the pumped water flow creates bubbles in the water in the column which, after being carried toward the bottom of the column by the water flow, rise through the column to produce foam at the water surface within the column. The pumped water exits the column through an opening at the bottom of the column. The bubble formation in this type of skimmer is wholly dependent upon the venturi effect at the pump outlet/air line interface which is difficult to regulate to achieve optimum bubble size and quantity.
In still another known type of foam fractionation skimming device, the bottom end of the water column is closed and water is drawn down through the column and out through a water line exiting near the bottom of the column. A first bubble forming gas discharge device is provided adjacent the bottom of the column to create and propel bubbles up through the column. A second bubble forming gas discharge device is provided in the water line exiting near the bottom of the column to create a water flow in the column counter to the rising bubbles in the column. Such a device is also limited by insufficient counterflow of water and bubbles.
Other known foam fractionation devices or systems use a water pump having an air line connected to the pump outlet to direct an air/water mixture into the bottom of a column or tube. The pumped water leaves the column through side openings in the column and the air bubbles rise to the top of the water surface within the column. It is difficult to separately monitor and regulate the air and water flow rates in such systems to achieve an optimum counterflow for efficient protein skimming by foam fractionation.